The use of hydrogen silsesquioxane resin to produce ceramic or ceramic-like coatings on electronic substrates is known in the art. Numerous methods have been developed to cure the hydrogen silsesquioxane resin to produce the coatings. Under known thermal processing and cure conditions (i.e., 1 minute hold at each of three serial hot plates followed by 1 hour in a furnace with a nitrogen atmosphere) dielectric constants of 2.9-3.0 are achieved.
Coatings having a dielectric constant of 2.9-3.0 are suitable for 0.25 micron and larger electronic devices. However, coatings having lower dielectric constants (Dk) are required for smaller device structures (i.e. 0.13-0.18 micron). Several methods have been proposed for curing the hydrogen silsesquioxane resin to produce a lower dielectric constant in the coating. However, these methods often require difficult and expensive processing to produce the low Dk coatings. For example, U.S. Pat. No. 5,441,765 to Ballance et al. discloses a method for producing coatings from hydrogen silsesquioxane resin wherein the cured coating has a Dk of 2.8 to 4.5. The process disclosed in U.S. Pat. No. 5,441,765 comprises applying the hydrogen silsesquioxane resin onto the device, heating the coated device for time sufficient to produce an Si--O containing ceramic coating and thereafter exposing the Si--O containing ceramic coating to an annealing atmosphere containing hydrogen gas.
U.S. Pat. No. 5,547,703 to Camilletti et al. discloses a method for producing low Dk coatings. The method comprises applying the hydrogen silsesquioxane resin on the electronic substrate; heating in ammonia and moisture; thereafter heating in anhydrous ammonia and finally heating in oxygen to anneal the coating. The Dk of the coatings produced by this method was reported to be between 2.42 and 4.92.
It has now been found that through thermal processing of hydrogen silsesquioxane resin that coatings having a dielectric constant of 2.7 to 2.9 can be produced. The thermal processing comprises curing the hydrogen silsesquioxane by first heating at a temperature of about 325.degree. C. to 350.degree. C. thereafter heating at a temperature of about 400.degree. C. to 450.degree. C. until the normalized SiH bond density is 50 to 80%.
It is therefore an object of this invention to show a method for curing hydrogen silsesquioxane resin to produce coatings having a dielectric constant of 2.7 to 2.9.